The present invention relates to energy cogeneration systems and, more particularly, to an energy cogeneration system and a method of controlling such a system which enables the heat energy of steam not needed at any given time for processing to be utilized for the generation of mechanical and/or electrical energy.
Some industrial processes require both large amounts of electrical power, and steam or heat energy for various other purposes. For example, paper mills require significant electrical energy as well as heat energy for other purposes, such as drying. It is not unusual for a plant of this nature to have its own electrical generation system, e.g., a steam driven turbo-alternator. And because waste heat is associated with the production of electricity from steam, systems have been designed not only to produce the desired electrical output but also to enable additional heat energy to be made available for other purposes. Systems of this type are often referred to as cogeneration systems. U.S. Pat. Nos. 2,893,926; 3,064,435; 3,233,413; 3,019,933; 3,233,412; 3,488,961; 3,367,111; 3,724,214; 3,391,539; and 4,042,809 describe systems of this general type.
It has been the practice in cogeneration systems to maintain the pressure of the headers or other steam distribution means for the processing units at generally constant set-points. This is accomplished by maintaining the turbine extraction and/or exhaust pressures which feed the headers at a constant (although sometimes adjustable) set-point, and furnishing any additional steam required by the headers to maintain the constant pressure directly from the steam supply through pressure reducing stations. It will be recognized, however, that the processing units fed by the headers may have variable demand for heat energy furnished by the steam. Because of such, it has been common to also include pressure reducing valves intermediate the headers and processing units, which valves are controlled by the demands of the individual processes associated therewith. Pressure throttling at this location, however, represents loss in available energy.